I know this is not questions you get every day ! but, I am very close to buying a very nice Cosmo Sport 110S, 10A, 1969. It is overall in very good condition, but there is some problems with the car running proberly the car has been at a Rotary specialist for many month to get this sorted, a week ago it came back to the owner, that of course believed the car now was as good as ever, but after she (yes the owner is a woman ) took it for a good testdrive, she is not happy with the result ! here is her experience:

For your information the car is running smoothly and starts without problem. Up to about 4000 rpm she feels fine, but then power drops off so in 4th with my foot almost on the floor she is only doing 80 kph!! Also as soon as you put the engine under pressure, clouds of white smoke out the exhaust!

So, do any of you guys have any thoughts about this ? what about the compression figures, does they seams ok for such a motor do you think ? I am really looking forward to hear of any thoughts, as I really really would like to help the owner sort things out, so I can bring her to my place soon

According to the Australian forum: http://ausrotary.com/ some people belive that 85 psi (5.8 bar) is ok for a Cosmo Sport 10A, 6mm onepice apexseal ! but I still miss someone really determine this, and as you write, they allso say that the loss of power over 4,000 rpm sounds like another fault. But again, the car will have to go back to a garage to determine if the problems is big or minor yes, it is Rotechniks in Reading, UK, that have had the car, and they allso got the car when it was first imported (2009) to the UK from Japan, so they really should know this car ! the strange thing is, why they delivered the car back to the owner this time, not running proberly ! I guess I should give them a call but as it is right now, the owner will NOT take it back to Rotechniks (even speak to them) and that is a problem I think ! I have forwarded the owner to Hayward Rotary, and they have told the owner that the compression figures is low, so it proberly needs a total rebuild which will be VERY costly, and the owner do not want to do that so what shall i belive and what shall I suggest

I might venture the opinion to buy it anyway, as there are a few options including transplants, as its not like there's a lot of Cosmo Sport on the market. Anywhere. Provided the price is reasonable that is... Neko.

First things first, engine troubles or not, jump on this car while you still can. The Cosmo is extremely rare, particularly the L10A. Plus, after having driven an L10B, I can safely say it's one of the most rewarding driving experiences to be had! Being a 1969, it should be a 10B, but it appears that between 1968 and 1970 there was a lot of transitional stuff going on and you could still have the first gen. motor. I'm still learning about these old Cosmos myself!

I don't know too much about rotary engines as I myself am learning as well. I do know that there are some notable differences between the L10A and L10B engines. Firstly, the transmission bellhousings are different, meaning you can't swap an L10B transmission onto an L10A engine or vice versa. The carburetors themselves are also different I believe. The biggest internal difference though is that the L10A uses rotors with 3 side seals whereas the L10B only has two side seals. This played an important enough role that no rotary since the L10A has used 3 side seals (I believe, I could be wrong though).

There are some options for swapping engines, but they aren't easy. Jay Leno swapped a 12A into his Cosmo but they had to fabricate a new crossmember from scratch and Bernard, Leno's mechanic, said they couldn't have fitted a 13B at all. Although with time and money, anything is possible.

As far as what could be causing the problems, I unfortunately do not know too much about trouble shooting rotaries, especially carb rotaries. However, even if the compression is low, it's fairly equal between all rotors, so I think it would be safe to say the the apex seals are alright. If there is a sealing problem, it would most likely be with the side seals. However, as that requires taking the engine completely apart, I would try everything else first, haha. Also, given that the engine only runs bad above a certain rpm or under high loads, I'd be willing to bet that something else is the culprit.

It appears that the 10A engine uses two ports per rotor for the intake. Interestingly, one port is closed off at low rpms for better torque. However, if this port were unable to open, it could severely hinder performance above 4 grand. Given that the carb will be dumping in as much fuel as possible but the engine will be receiving only half the amount of air it needs, the incredibly rich condition could be the cause of the smoke. That would also explain why it pulls cleanly until 4,000 rpm.

Also, these first gen. engines used dual distributors to handle the two plugs per cylinder. I would check the cap, rotor and plug wires on each distributor to make sure you're getting good ignition. If only one set of spark plugs is working, you could end up with a situation where at light loads, the one spark plug is sufficient but at heavy loads, the lack of a properly working leading trailing spark is causing massive amounts of fuel to go unburned and be forced through the exhaust. That could give you some smoke out the back as well and make it feel severely down on power at the higher rpms.

Well, I'm out of ideas, haha. Let us know how it goes and I'd love to see some pictures!

Firstly, I have now been confirmed about the model of the car : " Hi Rene, the engine in the piccies you've posted is an 0813 10A, which the engine designation in the L10B chassis'."

Cheers,Danny

So, it is NOT an earli L10A, but an second gen. L10B motor/chassis and from what I have found out, this is a good thing. Anyway, the motor still have theese problems, but I get more and more convinced it is not THAT bad, needing a total rebuild, new chambers, rotors etc, but "maybe" smaller internal problems as you mention, and maybe it is something "minor" like carb., timing, ignition, fuel etc. and that would be much much easier to deal with more people, have posted that the compression figures is not THAT bad, a little low at the rear chamber, but the numbers are even and the car starts fine when hot and idle nice, only above 4000 rpm with the the pedal to the metal it has the issues, I wish I could be in UK with the car to test it myself and get an idea of the problems !

I will give Rotechniks (the garage that have had the car) and talk to them about it all, and get a clue what they have done to the car, and what they think about the problems

The car is just so gorgeous and in overall great condition, I need it so bad

It appears that the 10A engine uses two ports per rotor for the intake. Interestingly, one port is closed off at low rpms for better torque. However, if this port were unable to open, it could severely hinder performance above 4 grand. Given that the carb will be dumping in as much fuel as possible but the engine will be receiving only half the amount of air it needs, the incredibly rich condition could be the cause of the smoke. That would also explain why it pulls cleanly until 4,000 rpm.

FYI all rotary carburetor engines operate this way from 10A to 13B.

Rene I'd like to correct a few untruths regarding any 10A engine, probably applied from the L10A to the last of the Rx3 10A's.

First of all pretty much everything seal wise required to rebuild a 10A is still available from Mazda. I know first hand because that is where I purchase my parts.

Owning any classic car is obviously going to need you thinking outside the square, whether it be a first generation Skyline, Savanna Rx3, Mazda R130, Datsun 1600 etc etc... I've been told a million times that I'm dreaming and will never get parts I'm after. I have organised quite a few non existent Savanna Rx3 parts, whether they be rubber, plastic injection moulded parts, engine parts, and my latest is brand new heated rear Savanna Rx3 windscreens including custom order all clear front windscreens (they normally have a blue band across the top). All done at reasonable cost, some parts are one offs which aren't shown anywhere.

From what I have seen on L10B engines there is not much to worry about regarding a rebuild unless it requires new rotor housings or new alloy side rotor housings. The rotors I saw first hand looked the same as R100 or early Rx3 rotors. I see no reason why you couldn't even use better sealing late model 10a Rx3 rotors. If the rotor stationary gear where different a competent machine shop could swap them over.

I've said this a million times to all the 10A detractors, Mazda still sell 90% of the seals required to build a 10A ! That's right you can still purchase 0 ring kits, apex seals, side seals, over size corner seals, water seals all from Mazda !!

While other parts such as apex spings are not available from Mazda they are still easy to find for reasonable money. There is a guy in Australia that sells the better sealing 2 piece 10a apex seals with springs for approx $500 or there abouts. That is cheaper than buying the equivalent 12a and 13B parts from Mazda. Mazda charge approx 400 - 450 for a set of 6 single single piece apex seals so that makes his price a bargain if you ask me. PM Mo's (user ID) if you are interested.

Other parts such as paper gaskets which would be unique on the L10B can easily be manufactured. We do this on for some of the later model twin distributor engines as not all gaskets are available. Not hard to do at all. The main problem with some of the new generation mechanics and the like is unless it comes out of a packet it's in the too hard basket. Rotor bearing and stationary gear bearings can be custom made to suit with little trouble. I see no reason once you know the required clearances, why you couldn't have a set of 12a or 13b bearings machined down.

Again there is nothing hard about building a 10a engine, most parts are available new (sealing parts). For the L10B your biggest concern would be the availability of the unique rotor housings. If they are screwed you will have a hell of a time locating a set. Same goes with the side alloy rotor housings although that would be less of a problem given that I see there is a guy in Europe making his own for a custom built quad rotor motor. Racing Beat also sell custom 12a / 13b alloy side rotor housings. What I'm getting at with these particular parts is that there are avenues available. I can think of 2 Australian engineering shops that could possibly be interested in making one off sets.

For me at least I don't believe in doing engine swaps because something is rare for the future generation to appreciate argument.... screw that !!! If I outlay some serious dollars I'm going to enjoy it for what it is and often as I like regardless of how unique or rare it is. If it blows up I'll worry about it then, there are always options.

Like others have said it sounds like a carb problem, I'd also take Danny's advice and have it properly tuned and not pull it apart until it's well and truely worn out And goes no longer. I just wanted to add that if the rotor housings and alloy side rotor housing are fine you'll have no trouble rebuilding the engine, 10A seal parts are not difficult to find. Joining some Cosmo Sport club would go a long way to prevent you from reinventing the wheel. Last I checked Europe, Australia and US still have good in house fabrication, machine and engineering shops all screaming for business from serious people in hard economic times. No one said owning any classic car was going to be convenient !

It appears that the 10A engine uses two ports per rotor for the intake. Interestingly, one port is closed off at low rpms for better torque. However, if this port were unable to open, it could severely hinder performance above 4 grand. Given that the carb will be dumping in as much fuel as possible but the engine will be receiving only half the amount of air it needs, the incredibly rich condition could be the cause of the smoke. That would also explain why it pulls cleanly until 4,000 rpm.

FYI all rotary carburetor engines operate this way from 10A to 13B.

Rene I'd like to correct a few untruths regarding any 10A engine, probably applied from the L10A to the last of the Rx3 10A's.

First of all pretty much everything seal wise required to rebuild a 10A is still available from Mazda. I know first hand because that is where I purchase my parts.

Owning any classic car is obviously going to need you thinking outside the square, whether it be a first generation Skyline, Savanna Rx3, Mazda R130, Datsun 1600 etc etc... I've been told a million times that I'm dreaming and will never get parts I'm after. I have organised quite a few non existent Savanna Rx3 parts, whether they be rubber, plastic injection moulded parts, engine parts, and my latest is brand new heated rear Savanna Rx3 windscreens including custom order all clear front windscreens (they normally have a blue band across the top). All done at reasonable cost, some parts are one offs which aren't shown anywhere.

From what I have seen on L10B engines there is not much to worry about regarding a rebuild unless it requires new rotor housings or new alloy side rotor housings. The rotors I saw first hand looked the same as R100 or early Rx3 rotors. I see no reason why you couldn't even use better sealing late model 10a Rx3 rotors. If the rotor stationary gear where different a competent machine shop could swap them over.

I've said this a million times to all the 10A detractors, Mazda still sell 90% of the seals required to build a 10A ! That's right you can still purchase 0 ring kits, apex seals, side seals, over size corner seals, water seals all from Mazda !!

While other parts such as apex spings are not available from Mazda they are still easy to find for reasonable money. There is a guy in Australia that sells the better sealing 2 piece 10a apex seals with springs for approx $500 or there abouts. That is cheaper than buying the equivalent 12a and 13B parts from Mazda. Mazda charge approx 400 - 450 for a set of 6 single single piece apex seals so that makes his price a bargain if you ask me. PM Mo's (user ID) if you are interested.

Other parts such as paper gaskets which would be unique on the L10B can easily be manufactured. We do this on for some of the later model twin distributor engines as not all gaskets are available. Not hard to do at all. The main problem with some of the new generation mechanics and the like is unless it comes out of a packet it's in the too hard basket. Rotor bearing and stationary gear bearings can be custom made to suit with little trouble. I see no reason once you know the required clearances, why you couldn't have a set of 12a or 13b bearings machined down.

Again there is nothing hard about building a 10a engine, most parts are available new (sealing parts). For the L10B your biggest concern would be the availability of the unique rotor housings. If they are screwed you will have a hell of a time locating a set. Same goes with the side alloy rotor housings although that would be less of a problem given that I see there is a guy in Europe making his own for a custom built quad rotor motor. Racing Beat also sell custom 12a / 13b alloy side rotor housings. What I'm getting at with these particular parts is that there are avenues available. I can think of 2 Australian engineering shops that could possibly be interested in making one off sets.

For me at least I don't believe in doing engine swaps because something is rare for the future generation to appreciate argument.... screw that !!! If I outlay some serious dollars I'm going to enjoy it for what it is and often as I like regardless of how unique or rare it is. If it blows up I'll worry about it then, there are always options.

Like others have said it sounds like a carb problem, I'd also take Danny's advice and have it properly tuned and not pull it apart until it's well and truely worn out And goes no longer. I just wanted to add that if the rotor housings and alloy side rotor housing are fine you'll have no trouble rebuilding the engine, 10A seal parts are not difficult to find. Joining some Cosmo Sport club would go a long way to prevent you from reinventing the wheel. Last I checked Europe, Australia and US still have good in house fabrication, machine and engineering shops all screaming for business from serious people in hard economic times. No one said owning any classic car was going to be convenient !

Hello gypsy

Thank you so much for your reply and all your great info this calms me a bit to know that actually most parts, for rebuilding the L10B motor in "my" Cosmo is not that impossible to find ! as you write, I can only hope it is not anything housing related I have once again, asked the seller to testdrive the car, and give me all the issues when driving/starting/ideling etc. and then talk to Rotechniks and get a more clear picture if it is "only" minor issues or it really request a total rebuild ! I know that, maybe it will not be that long into the future before it requires a rebuild (hopefully NOT housing) but that is to expect (it has 109.000 km on the clock) and then just enjoy it for that long my dilemma right now is, how much to offer the seller with that in mind that it MAYBE need a total rebuild

I try to post some pics, but can not ? it tells me this "Sorry, the board attachment quota has been reached." what does this means ?

Rule of thumb, if the engine starts reasonably easily when the engine is cold AND when it is hot, then it's serviceable i.e. probably not worth worrying too much about. If it struggles to restart when hot, then there's likely low compression and it will need a rebuild.

I think you have to host your pictures elsewhere (Flickr, Google+ or similar) and then link them here, not sure though.